1. Field of the Invention
The present invention relates to a method for etching and a method for manufacturing a thin film element employing the method for etching. As the thin film element, a thin film transistor can be given, for example. Note that in this specification, any device including a thin film element in which a semiconductor layer is provided is referred to as a semiconductor device.
2. Description of the Related Art
In recent years, semiconductor devices have been necessary for our life. Thin film elements such as thin film transistors included in such semiconductor devices are manufactured by forming a thin film over a substrate and processing the thin film into a desired shape by etching or the like. Such a method for manufacturing a thin film element is applied to liquid crystal display devices (e.g., liquid crystal televisions), for example.
In thin film transistors of conventional liquid crystal televisions, amorphous silicon films are often used as semiconductor films. This is because structures of thin film transistors formed of amorphous silicon films are thought to be manufactured with relative ease.
However, when the current circumstances of moving images (e.g., watching movies and sports in 3D) is taken into account, sharpness of moving images in a liquid crystal television using amorphous silicon films is insufficient; therefore, thin film transistors having high carrier mobility which responds at high speed are under development. For this reason, microcrystalline silicon films have been developed. As a reference disclosing a thin film transistor using a microcrystalline silicon film, Patent Document 1 can be given, for example.
In Patent Document 1, a thin film transistor having a high field effect mobility and high on-state current is disclosed.